1. Field of the Invention
The present invention generally relates to tubular connectors. In particular, the present invention relates to a method of connecting tubulars in such a way that the connection is prevented from becoming unmade in response to expansion of the tubulars. More particularly, the present invention provides a tubular connection wherein there is at least one concentric interlocking ring profile.
2. Description of the Related Art
In order to access hydrocarbons in subsurface formations, it is typically necessary to drill a bore into the earth. The process of drilling a borehole and of subsequently completing the borehole in order to form a wellbore requires the use of various tubular strings. These tubulars are typically run downhole where the mechanical and seal integrity of the jointed connections are critically important both in the original make-up of the tubulars and during expansion of the tubulars.
Typically threaded connections are used to connect multiple tubular members end-to-end. This is usually accomplished by providing tubulars that have a simple male to female threaded connection. The male end is generally referred to as a pin, and the female end as a box. These tubulars are connected, or “made-up,” by transmitting torque against one of the tubulars while the other tubular is held stationary. Torque is transmitted in a single direction in accordance with the direction corresponding with connection make-up. Any torque applied to the joint in the make-up direction will have the effect of continuing to tighten the threaded joint.
When running tubulars there is sometimes a requirement to run jointed tubulars that will later be expanded by various types of expansion mechanisms. These tubulars are typically run downhole where the mechanical and seal integrity of the connections, or joint, are critically important both in the original and expanded state of the tubular. The current methods of achieving this is by the design of modified threaded connections which can be applied and handled in the same way as conventional oil-field tubulars, i.e., stabbed into each other and screwed together by right hand or left hand rotation and then finally torqued up to establish the seal integrity.
This method of connecting tubulars, though a reliable means of connecting non-expanding tubulars, is proving to be problematic when these tubulars are expanded. The reasons for this being mainly due to the changes in geometry of the connection during expansion due to the stresses applied at the threads, or joint area. Conventional tubulars expanded at the joint may, for instance, disengage allowing the lower tubing to fall into the wellbore.
It is well known and understood that during the expansion of solid wall tubulars that the material in the tubing wall is plastically deformed in more than just the circumferential sense. In order for a tubular to increase in diameter by plastic deformation, the material to make up the additional circumferential section of wall in the larger diameter must come from the tubing wall itself either by reduction in wall thickness, or by reduction in tubular length, or a combination of both. In the plain wall section of the tubular this process will normally take place in a relatively controlled and uniform way, however, at the point of a threaded connection the changes in wall section which are required in order to form the thread will introduce a very complex and non-uniform stress and deformation during and after expansion, which will significantly change the thread form and compromise the connection integrity both in terms of its mechanical strength and sealing capability. Additionally, the larger elastic deformation caused by the reduced sections of the tubing wall at the roots of the thread will introduce much higher stresses than in other areas of the expanded tubular. This in turn may lead to joint failure due to these stresses approaching or exceeding the ultimate strength of the tubing material or by introduction of short cycle fatigue caused by the cyclic nature of some expansion processes being applied at these high stress levels.
The objective of the present invention is to resolve many of the problematic areas associated with the expansion of threaded connections. The present invention consists of replacing the conventional thread connections with the introduction of one or more interlocking ring profiles which can be engaged by either the partial plastic deformation of the pin, the partial plastic deformation of the box, or by a combination of the two processes.
This innovative concept of using plastic deformation of the mating parts of the jointed system being described in this invention provides the essential step to making this invention a practical and novel solution to expandable tubular connections. The typical materials used for expandable tubulars must of course be ductile, which in turn means that the connection profiles, also referred to as formations, in this invention should not be highly stressed during the stab-in part of the joint make-up process. To avoid this possibility the connection profiles are designed such that they will pass over each other with little or no induced stress and are located in longitudinal alignment by the introduction of a mating or stop shoulder at the top of the box, or pin, and or shoulders within the joint.
In this position the joint can be made-up by the application of an internal or external force sufficient to cause yield of the pin in expansion or the box in compression. For increased strength it may be desirable for the tubulars to be internally or externally upset at their ends where these joints are machined. However, in a constant wall thickness tubular where the finished expanded tubular must be externally and internally flush, it may be desirable to slightly swedge the pin inwardly or swedge the box outward.
Additionally, it may be preferable to incorporate one or more torque screws. The torque screw would preferably be set externally and extend through the box into the pin. These screws would preferably be positioned near the tubulars' thread profile. Further, by incorporating torque screws, the torque rating of the threads would be greatly increased. In addition to, or as an alternative to, torque screws, the tubulars' walls could be cut with locking castellations or other anti-torque locking means as known to those in the arts.
The handling of these jointed tubulars would require specialized equipment on the rig floor to plastically deform the connections on make-up, and one approach to this is shown in FIG. 8, wherein the pin is being expanded internally. The benefit of this approach would be that the growth of the box could be measured and used for quality assurance of joint make-up and integrity before running the made-up tubulars down hole.
Once made-up these joints would not be disconnectable other than by cutting at or close to each joint. However, systems have been proposed which can easily achieve this on the rig floor in a safe, reliable and timely fashion. One such system introduces rolling element cutters to conventional rig power tongs which could be used to simply cut the tubular in the same way that a plumber cutter cuts copper tubing.